Scan architecture for interconnect testing in 3d integrated circuits

ABSTRACT

In one embodiment, a device comprises: a first die having disposed thereon a first plurality of latches wherein ones of the first plurality of latches are operatively connected to an adjacent one of the first plurality of latches; and a second die having disposed thereon a second plurality of latches wherein ones of the second plurality of latches are operatively connected to an adjacent one of the second plurality of latches. Each latch of the first plurality of latches on said first die corresponds to a latch in the second plurality of latches on said second die. Each set of corresponding latches are operatively connected. A scan path comprises a closed loop comprising each of said first and second plurality of latches. One of the second plurality of latches is operatively connected to another one of the second plurality of latches via an inverter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. Application No.16/724,787, filed Dec. 23, 2019, which is a divisional of U.S. Pat.Application No. 15/171,531, filed on Jun. 2, 2016, now U.S. Pat.10,539,617, each of which are incorporated by reference herein in theirentireties.

BACKGROUND

The 3D-IC approach uses a combination of standard single damascenetechniques, wafer thinning, and direct Cu—Cu thermo-compression bonding.Hybrid bonding is a cost-effective, die-to-wafer integration processesfor vertical stacking and high density die-to-die interconnecting.

In general, direct hybrid bonding is compatible with both die-to-die(D2D) and wafer-on-wafer (WoW) bonding. In direct hybrid bonding, a dualdamascene copper and silicon oxide hybrid interface between dies servesas both the full-area substrate bonding mechanism and the electricalconnection between pads and/or vias on respective dies.

Design-for-Testing or Design for Testability (“DFT”) refers tointegrated circuit design techniques that add certain testabilityfeatures to a hardware product design. The DFT features make it easierto develop and apply various manufacturing tests for the designedhardware. The purpose of manufacturing tests is to validate that thehardware products contain no manufacturing defects that could adverselyaffect the product’s proper functioning. Scan chain is one example of atechnique implemented in a DFT process.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. Variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a cross-sectional view of the hybrid bonded 3DIC inaccordance to some embodiments.

FIG. 1B is a schematic diagram of a serial cross-bar scan architecturein accordance with some embodiments.

FIG. 2A is a schematic diagram of a serial cross-bar scan architecturewith D flip-flops and scan flops in accordance with some embodiments.

FIG. 2B is a schematic illustration of a scan flip-flop in accordancewith some embodiments.

FIG. 2C is a schematic illustration of a D flop in accordance with someembodiments.

FIG. 3 is a schematic diagram of a serial cross-bar scan architecturewith D flip-flops and multiplexers in accordance with some embodiments.

FIG. 4 is a schematic diagram of a scan architecture with non-equalnumber of inputs and outputs between dies in accordance with someembodiments.

FIG. 5 is a schematic diagram of a scan architecture with connectionsbetween flip-flops which are within the same die but not adjacent toeach other in accordance with some embodiments.

FIG. 6 is a schematic diagram of a scan architecture with multiple scanoutputs in accordance with some embodiments.

FIG. 7 is a schematic diagram of a scan architecture with sharedfunctional flip-flops in accordance with some embodiments.

FIG. 8 is a schematic diagram of a scan architecture with level shiftersin accordance with some embodiments.

FIG. 9A is a schematic diagram of a scan architecture with on-chip testgeneration and comparison in accordance with some embodiments.

FIG. 9B is a schematic diagram of a test pattern generator for on-chiptest generation in accordance with some embodiments.

FIG. 9C is a schematic diagram of a test response comparison unit foron-chip test generation and comparison in accordance with someembodiments.

FIG. 10 is a schematic diagram of a deterministic circular built-inself-test architecture in accordance to some embodiments.

FIG. 11 is a block diagram of a deterministic circular built-inself-test architecture in accordance with some embodiments.

FIG. 12 is a schematic diagram of a fault free circuit of fourflip-flops and its corresponding logic table in accordance with someembodiments.

FIG. 13 is a schematic diagram of a circuit with a stuck-at-1 fault at afirst location of four flip-flops and its corresponding logic table inaccordance with some embodiments.

FIG. 14 is a schematic diagram of a circuit with a stuck-at-1 fault at asecond location of four flip-flops and its corresponding logic table inaccordance with some embodiments.

FIG. 15 is a schematic diagram of a circuit with a stuck-at-1 fault at athird location of four flip-flops and its corresponding logic table inaccordance with some embodiments.

FIG. 16 is a schematic diagram of a circuit with a stuck-at-1 fault at afourth location of four flip-flops and its corresponding logic table inaccordance with some embodiments.

FIG. 17 is a schematic diagram of a circuit with a stuck-at-0 fault at afirst location of four flip-flops and its corresponding logic table inaccordance with some embodiments.

FIG. 18 is a logic table of a circuit with 7 flip-flops under holdfaults in accordance with some embodiments.

FIG. 19 is a logic table of a circuit with 7 flip-flops under setupfaults in accordance with some embodiments.

FIG. 20 is a schematic diagram of a fault-free on-chip scan-chain with 7flip-flops and its corresponding logic waveforms in accordance with someembodiments.

FIG. 21 is a schematic diagram of an on-chip scan-chain having a holdviolation with 7 flip-flops and its corresponding logic waveforms inaccordance with some embodiments.

FIG. 22 is a schematic diagram of an on-chip scan-chain having a setupviolation with 7 flip-flops and its corresponding logic waveforms inaccordance with some embodiments.

FIG. 23 is a flowchart illustrating the method for deterministiccircular built-in self-test in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matter.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature’s relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1A is a cross-sectional view of a hybrid bonded 3D stack inaccordance to some embodiments. The top die 100 includes a semiconductor(e.g., silicon) substrate 101, and the bottom die includes asemiconductor (e.g., silicon) substrate 201. Both the substrates 101 and201 include functional circuits in them. The functional circuits includeactive devices, such as transistors, shown in substrates 101 and 102 andinterconnects 110, 210 in each die. The interconnect layer 110 of thetop die 100 and the interconnect layer 210 of the bottom die 200 areconnected by hybrid bonding structures 301 and 302. FIG. 1B is aschematic diagram of a serial cross-bar scan architecture in accordancewith some embodiments. The serial cross-bar scan architecture includesan upper die 1100 and a lower die 1200. The upper die 1100 is stackedabove the lower die 1200. According to some embodiments, the bondingbetween the upper die 1100 and the lower die 1200 is hybrid bonding,which is a cost-competitive solution for vertical stacking and provideshigh density die-to-die interconnect. According to some embodiments, thepitch between the interconnections is, for example, 1um or less. Hybridbonding reduces leakage, power consumption and device footprint comparedto a 3DIC in which connections between active devices on stacked diesinclude through-substrate-vias (TSV). Each of the lines 1302, 1303,1304, ... 1309 represents a combination of one or more vias and/or oneor more pads in each of the upper die 1100 and lower die 1200.

In other embodiments (not shown), interconnections between stacked diesin the 3DIC include TSVs. In other embodiments (not shown), the 3DIC isa stacked CMOS package, in which interconnections between tiers includeinter-tier vias (ITV) also referred to as inter-level vias (ILV).

Some embodiments of a scan chain include the following set of signals inorder to control and observe the scan mechanism. Scan_In (SI) andScan_Out(SO) are the input and output of a scan chain, respectively. Ashift enable pin (SE) is a special signal that is added to a design.When SE is asserted, every latch in the scan chain is connected to arespective bit of a shift register. . A clock signal is used forcontrolling all the latches, or flip-flops, in the chain during testingof the IC. An arbitrary test pattern (for example, a vector of randomzeroes and ones) can be entered into the chain of latches, and the stateof every latch can be read out.

As shown in FIG. 1B, the architecture includes a wrapper around theinterface between the upper die 1100 and lower die 1200. The wrapperincludes a respective wrapper cell (e.g., flip-flops 1121-1128 and1221-1228) in each of the dies 1100, 1200 on each side of each inter-dieconnection 1302-1309, Additional intra-die connections 1151-1154 and1251-1253 are added to form a scan path 1900, which functions as a shiftregister during scan chain testing. The scan shift path (scan path) isthe route that the signal follows during a scan test. According to someembodiments, the scan shift path includes latches in the upper die andthe lower die, their corresponding interconnections between dies andconnections between latches in the same die. According to someembodiments, the scan shift path starts with a scan input, and ends withat least one scan output. The scan path includes a continuouslyconnected set of latches and interconnections between and within dies,for shifting data from the scan input to the scan output.

The upper die 1100 includes a test and clock control unit 1110 and aplurality of flip-flops 1121, 1122, 1123, 1124, 1125, 1126, 1127 and1128. According to some embodiments, the flip-flops 1121 ... 1128 are ofthe same type, according to other embodiments, the flip-flops 1121 ...1128 are of two or more different types. The test and clock control unit1110 transmits a clock signal CLK1 through the line 1140. The clocksignal CLK1 controls the flops 1121 ... 1128 through 1141, 1142, 1143,1144, 1145, 1146, 1147 and 1148, respectively. The test and clockcontrol unit 1110 controls the flip-flops 1121 ... 1128 through 1131,1132, 1133, 1134, 1135, 1136, 1137 and 1138, respectively. The output ofthe flip-flop 1121 is transmitted to the input of flip-flop 1122 throughline 1151; the output of the flip-flop 1123 is transmitted to the inputof the flip-flop 1124 through line 1152; the output of the flip-flop1125 is transmitted to the input of the flip-flop 1126 through line1153; the output of the flip-flop 1127 is transmitted to the input ofthe flip-flop 1128 through line 1154.

Similarly, the lower die 1200 includes a test and clock control unit1210 and a plurality of flops 1221, 1222, 1223, 1224, 1225, 1226, 1227and 1228. According to some embodiments, the flip-flops 1221 ... 1228are of the same type of flip-flops, according to other embodiments, theflip-flops 1221 ... 1228 are of different types of flip-flops. The testand clock control unit 1210 transmits a clock signal CLK2 through line1240, the clock signal CLK2 controls the flip-flops 1221 ... 1228through 1241, 1242, 1243, 1244, 1245, 1246, 1247 and 1248 respectively.The test and clock control unit 1210 controls the flip-flops 1221 ...1228 through 1231, 1232, 1233, 1234, 1235, 1236, 1237 and 1238respectively. The scan in signal 1301 is transmitted to the flip-flop1221. The output of the flip-flop 1222 is transmitted to the input offlip-flop 1223 through line 1251, the output of the flip-flop 1224 istransmitted to the input of the flip-flop 1225 through line 1252, theoutput of the flip-flop 1226 is transmitted to the input of theflip-flop 1227 through line 1253, the output of the flip-flop 1228 isthe scan out 1310. The test and clock control unit 1110 in the upper die1100 and the test and clock control unit 1210 in the lower die 1200communicate through line 1312.

An inter-die scan path 1900 designated by dashed line can be created byembedding at least one functional path in a scan shift path. Afunctional path is a path that is not dedicated to the scan chain fortesting purposes only, but rather is included in a functional circuitthat performs other non-testing functions. The functional path caninclude one or more interconnect lines and/or interconnect vias withinone of the dies. According to some embodiments, the embedded functionalpath includes other passive and/or active elements. The scan chain actsas a shift register during scan chain testing. In some embodiments, afunctional path connected to a circuit is connected to a multiplexer inthe scan shift path, and the multiplexer can be used to select either atest pattern input or a signal on the functional path connected to thefunctional circuit This allows scan chain testing across functionalpaths, in addition to the interconnections shown in FIG. 1B. Theinter-die scan path 1900 starts at the scan in signal 1301, then passesthrough, in order, flip-flop 1221, line 1302, flip-flop 1121, , line1151, flip-flop 1122, line 1303, line 1303, flip-flop 1222, line 1251,flip-flop 1223, line 1304, flip-flop 1123, line 1252, flip-flop 1124,line 1305, flip-flop 1224, line 1252, flip-flop 1225, line 1306,flip-flop 1125, and so forth. The inter-die scan path 1900 crossesbetween the upper die 1100 and the lower die 1200 until it reaches theflip-flop 1228 in the lower die 1200. The output of the flip-flop 1228is transmitted to the scan out 1310 to complete the inter-die scan path1900. As discussed above, a functional path is a path included in acircuit that performs non-scan-chain-testing functions, and such afunctional path is not dedicated to the scan chain wrapper cellstructure. Functional paths 1302, 1303, 1304, 1305, 1306, 1307, 1308 and1309 are embedded in the shift path of scan path 1900. CLK1 and CLK2 arekept the same and synchronized during the scan. According to someembodiments, the shift clock frequency is swept during scan chaintesting, to check timing-related defects caused by weak short or opensand DC defects.. According to some embodiments, the clock frequenciesCLK1 and CLK2 are swept through a range from 50 MHz to 2 GHz during scanchain testing. According to some embodiments, dummy connections areadded to form a continuous chain of wrapper cells between the upper andlower dies, effectively forming a single shift register that is usedduring scan chain testing. According to some embodiments, testing isperformed through shift operation at several different clockfrequencies. Each time the clock is changed to a new frequency, a newclock leading edge occurs. Each flip-flop can use the leading edge ofthis new clock to trigger a capture. At the leading edge of this newclock, the flip-flops output the captured value from their respective Dinputs to their respective Q outputs, shifting the data along the shiftpath. As a result, there is no requirement for a separate capturefunction to trigger the capture by setting scan enable (SE = 0).According to some embodiments, scan chain test patterns are generated,for example, by a general purpose processor programmed to execute aprogram such as an automatic test pattern generator (ATPG). If the scanchain test fails at low speed, then a hard defect is detected. If thescan chain test fails at high speed, then a resistive or weak defect isdetected. According to some embodiments, a speed lower than 50 MHz isconsidered as low speed, the range between 50 MHz and 500 MHz isconsidered as high speed, 500 MHz and above is considered very highspeed. If the 3DIC fails the DC test, this is an indication that the3DIC contains at least one hard open circuit or short circuit defect. Ifthe 3DIC passes the DC test, then the AC test is performed at a firstfrequency. If the 3DIC passes the AC test at the first frequency, theshift frequency is increased and the AC test is repeated. One or moreiterations of the shift frequency increase and testing are repeated,until the 3DIC fails the AC test. The maximum frequency at which the3DIC passes the scan chain test. The presence of AC defect is computedby correlating the measured passing frequency and expected shiftfrequency. Test or shift frequency is the speed at which data istransferred from the bottom die 1200 to the top die 1100 through theinterconnections or the functional paths. As a result, the maximumpassing shift frequency reflects the actual speed of theinterconnections, or the functional path. FIG. 2A is a schematic diagramof a serial cross-bar scan architecture with D flops and scan flops inaccordance with some embodiments. The schematic diagram in FIG. 2 hasthe same sequence of connections 2302-2308 as shown in the embodiment inFIG. 1 , but the embodiment of FIG. 2 has two different kind offlip-flops. Flip-flops 2121, 2123, 2125, 2127, 2222, 2224, 2226 and 2228are D flops, while flops 2122, 2124, 2126, 2128, 2221, 2223, 2225 and2227 are “scan flip-flops.” The scan flip-flops 2800 of FIG. 2 allinclude a regular D flip-flop 2801 and a multiplexer 2802, as shown inFIG. 2B. The scan flops are used for inter-die scan testing and the Dflops are used for intra-die scan testing. The scan chain follows thesame shift path as the implementation in FIG. 1 . The details of the Dflops and the scan flops are illustrated in FIG. 2B.

FIG. 2B is a schematic illustration of a scan flip-flop, and FIG. 2C isa schematic illustration of a D flop in accordance with someembodiments. The scan flip-flop 2800 includes a regular D flip-flop 2801and a multiplexer 2802. The multiplexer 2802 has two inputs: the scaninput 2803 and the functional path input 2804. The output 2805 of themultiplexer 2802 is transmitted to the D flip-flop 2801, the output 2806of the D flip-flop is transmitted to another die by way of one or moreconductive vias and/or one or more conductive pads (not shown). Incomparison, D flip-flop 2901 receives a functional path signal from apath included in a functional circuit, which is located on another die,by way of an input 2902 and the D flip-flop 2901 has an output 2903. Afunctional circuit is a circuit in one of the dies that performs afunction and is not exclusively used during scan chain testingoperations.

FIG. 3 is a schematic diagram of a serial cross-bar scan architecturewith D flops and multiplexers in accordance with some embodiments. Theembodiment in FIG. 3 is similar to the embodiment in FIG. 1 , exceptthat in the embodiment of FIG. 3 , multiplexers are used to selecteither a functional path signal from a connecting path with a functionalcircuit in the same die as the flip-flop or a scan chain value outputfrom the flip-flop. The value selected by the multiplexer is thenprovided to the other die.

According to some embodiments, a multiplexer 3161 is inserted at theoutput of the flip-flop 3122. One input 3161A of the multiplexer 3161receives the output of the flip-flop 3122, the other input 3161B of themultiplexer 3161 receives a signal from a functional path of afunctional circuit 3170 within the upper die 3100. The output of themultiplexer 3161 is transmitted through inter-die functional path 3303to flip-flop 3222 in the lower die 3200. Similarly, multiplexers 3162,3163 and 3164 are inserted at the outputs of respective flops 3124, 3126and 3128 in the upper die 3100, and multiplexers 3261, 3262, 3263 and3264 are inserted at the outputs of the respective flops 3221, 3223,3225 and 3227 in the lower die 3200. The multiplexer inputs 3161B,3162B, 3163B and 3164B are all connected to a functional path of afunctional circuit in the upper die 3100, the functional circuit 3170.Similarly, the multiplexers’ inputs 3261B, 3262B, 3263B and 3264B in thelower die 3200 are all connected to another functional circuit (notshown) in the lower die 3200. The scan path 3900 of the scan chain isindicated by a dashed line.

FIG. 4 is a schematic diagram of a serial cross-bar scan architecturewith non-equal number of inputs and outputs between dies in accordancewith some embodiments. For example, the upper die 4100 and lower die4800 can be of different types. In an example, shown in FIG. 4 , theupper die 4100 has one inter-die output 4309 illustrated in solid line,but the lower die 4800 has four inter-die outputs 4302, 4304, 4306, 4308illustrated in solid lines. Compared to FIG. 1 , there are only fiveflops in the upper die, four of which are D flops (i.e., 4121, 4122,4123 and 4124) receiving inputs from lower die; the fifth flip-flop 4125of the upper die is a scan flip-flop which provides an output to thelower die. The lower die has five corresponding flops, four of which arescan flops (i.e., 4221, 4222, 4223 and 4224) providing outputs tocorresponding D flops (i.e., 4121, 4122, 4123 and 4124) in the upperdie; The fifth flip-flop 4225 in the lower die is a D flip-flopreceiving an input from scan flip-flop 4125 in the upper die.

In some embodiments, as shown in FIG. 4 , dummy interconnects 4303, 4305and 4307 (illustrated in dashed lines) are added to enable flow of scanchain test data between the upper die and the lower die. According tosome embodiments, dummy connections are added to form a continuous chainof wrapper cells between the upper and lower dies, effectively forming asingle shift register that is used during scan chain testing. A dummyconnection is an interconnection provided for scan chain testing, butnot used by any functional circuits during other operations (besidesscan chain testing). Because the dummy interconnections between die areonly used during scan chain testing (but not during normal operations),the adjacent wrapper cells providing signals to the dummyinterconnections do not use multiplexers to select between a testpattern input signal and a functional path input signal. The adjacentwrapper cells providing signals to the dummy interconnections cancontain a latch without a multiplexer. The dummy interconnects 4303,4305, and 4307 allow the flip-flops 4121-4125 and 4201-4205 to operateas a shift register during scan-chain testing. The scan path 4900 of thescan chain is illustrated by arrows in FIG. 4 , and includes, in order,flip-flops 4201, 4121, 4222, 4122, 4223, 4123, 4224, 4124, 4125 and4225.

FIG. 5 is a schematic diagram of a scan architecture with connectionsbetween flip-flops which are within the same die but not adjacent toeach other, in accordance with some embodiments. There are three D flops(5121, 5122 and 5124) in the upper die 5100 for receiving inputs fromcorresponding scan flops (i.e., 5221, 5222, 5224) in the lower die 5200.There are two scan flip-flops (5123 and 5125)in the upper die 5100 forsending outputs to the corresponding D flip-flops (5223 and 5225) in thelower die 5200. In this case, the flip-flop immediately adjacent to theD flip-flop 5121 within the upper die 5100 is another D flip-flop 5122.In some 3DIC designs it may be impractical or undesirable for thedesigner to insert a dummy interconnect to direct the output of Dflip-flop 5121 to the adjacent scan flip-flop 5222 in the lower die5200. Using a method as shown in FIG. 5 , the output 5303 of the Dflip-flop 5121 can be directed to a non-adjacent scan flip-flop (e.g.,5123) in the upper die, such that the output 5304 of the non-adjacentflip-flop 5123 crosses to the lower die 5200 and is connected to a Dflip-flop 5223 in the lower die 5200. Similarly, the output 5305 of theD flip-flop 5223 is directed to a scan flip-flop 5222 in the lower die5200. The output 5306 of the scan flip-flop 5222 then crosses to theupper die 5100 and connects to a D flip-flop 5122. The output 5307 ofthe D flip-flop 5122 crosses to the lower die 5200 again the connects toa non-adjacent scan flip-flop 5224 in the lower die 5200. The shift paththen continues to cross to the upper die 5100 through 5308 to reach Dflip-flop 5124, then through 5309 to scan flip-flop 5125. After crossingto the D flip-flop 5225 in the lower die 5200 through 5310, the shiftpath completes with scan out 5311. The scan path 5900 of the scan chainis illustrated with dashed line. The scan path 5900 includes, in order,flip-flops 5221, 5121, 5123, 5223, 5222, 5122, 5224, 5124, 5125 and5225.

FIG. 6 is a schematic diagram of a scan architecture with multiple scanoutputs in accordance with some embodiments. The embodiment in FIG. 6 issimilar to the embodiment in FIG. 2A except that instead of having onlyone scan out 2310, there are four different taps for scan outputs 6310A,6310B, 6310C and 6310D. The first scan output 6310A is taken from thepath between the D flip-flop 6222 and the scan flip-flop 6223, thesecond scan out 6310B is taken from the path between the D flip-flop6224 and the scan flip-flop 6225, the third scan out 6310C is taken fromthe path between the D flip-flop 6226 and the scan flip-flop 6227, andfinally the fourth scan out 6310D is taken from the output of the Dflip-flop 6228. Multiple scan outputs permit the user of a largervariety of fault diagnosis algorithms, to identify the specific locationof a defect. The scan path 6900 of the scan chain is illustrated withdashed line, and is the same as that discussed above with reference toFIG. 2A.

FIG. 7 is a schematic diagram of a scan architecture with sharedfunctional flip-flops in accordance with some embodiments. Theembodiment in FIG. 7 is similar to the embodiment in FIG. 2A except thatintra-die flip-flops 7123, 7125, 7222 and 7224 are “shared functionalflip-flops” rather than dedicated D flip-flops. A shared functionalflip-flop is used during scan chain testing, and is also used by afunctional circuit within one of the dies while that die is performingan operation other than scan chain testing. The D flip-flops 7123 and7125 are part of a functional circuit 7810 in the upper die. The Dflip-flops 7222 and 7224 are part of a logic unit 7820 in the lower die.The intra-die flops 7123, 7125, 7222 and 7224 are not dedicated for scanchain testing. Instead, each of the flip-flops 7123, 7125, 7222 and 7224are included in separate logic circuitry (e.g., in their own logic units7810 and 7820 respectively). Sharing flops for use both during scanchain testing and during normal operation is usually possible from afunctional point of view, but providing dedicated flip-flops for scanchain testing may simplify routing in some IC designs. In someembodiments, flip-flop sharing as shown in FIG. 7 can be used to reducedie size, for example, The scan path 7900 of the scan chain in FIG. 7 isillustrated with dashed line, and includes, in order, flip-flops 7221,7121, 7122, 7222, 7223, 7123, 7124, 7224, 7225, 7125, 7126, 7226, 7227,7127, 7228, and 7128.

FIG. 8 is a schematic diagram of a scan architecture with level shiftersin accordance with some embodiments. The embodiment in FIG. 8 is similarto the embodiment in FIG. 4 , with four D flip-flops, 8121, 8122, 8123and 8124, in the upper die 8100 for receiving inputs from scanflip-flops, 8221, 8222, 8223 and 8224, respectively, in the lower die8200, and a scan flip-flop 8125 in the upper die 8100 for sending signalto the D flip-flop 8225 in the lower die 8200. The scan path 8900 issimilar to the scan path 4900 in FIG. 4 , and includes flip-flops 8221,8121, 8222, 8122, 8223, 8123, 8224, 8124, 8125 and 8225. The differenceis that eight level shifters 8401, 8402, 8403, 8404, 8405, 8405, 8407and 8408 are inserted along the scan path 8900 in the connectionsbetween the upper die and the lower die. Although the level shifters8401-8408 are shown schematically between the dies 8100 and 8200, theindividual level shifters can be included within the upper die 8100and/or the lower die 8200. The implementation of level shifters betweenthe upper die and the lower die permits inclusion of dies having two ormore different voltage levels within the same 3DIC. When the upper dieand the lower die implement different technologies, their voltage levelsmay differ. According to some embodiments, with level shifters, an upperdie and lower die of different technologies can be stacked within thesame 3DIC. Level shifters can be included in any of the embodiments fromFIGS. 1 through 7 . The scan path 8900 of the scan chain is illustratedwith dashed line, and includes the flip-flops 8221, 8121, 8222, 8122,8223, 8123, 8224, 8124, 8125, and 8225.

FIG. 9A is a schematic diagram of a scan architecture with on-chip scanchain test data generation and comparison in accordance with someembodiments. The embodiment in FIG. 9 is similar to the embodiment inFIG. 3A, with eight flops, 9121, 9122, 9123, 9124, 9125, 9126, 9127 and9128 in the upper die 9100, and eight flops, 9221, 9222, 9223, 9224,9225, 9226, 9227 and 9228 in the lower die 9200. The test and clockcontrol unit 9210 is different from the test and clock controls 3110 and3210. Instead of receiving tests from scan in 3301 from outside theupper and the lower dies, according to some embodiments as shown in FIG.3A, test patterns are generated inside the test and clock control unit9210 in the die including the first flip-flop in the scan chain shiftpattern (e.g., the lower die 9200 in the example of FIG. 9 ). The scanchain test data sequence is generated on-chip and then transmitted tothe first flip-flop through interconnection 9301. Then a scan pathsimilar to scan path 3900 is followed, and the scan output 9310 istransmitted into the test and clock control unit 9210 where a comparisoncan be conducted on-chip. According to some embodiments, the on-chiptest generation and comparison facilitates scan chain testing withoutexternal test generation and comparison. In other embodiments, externaltest generation and comparison can reduce the time for test generationand comparison. The on-chip test generation and comparison can beimplemented to any of the embodiments in FIGS. 1 through 8 . Scan path9900 of the scan chain is illustrated with dashed line, and includesflip-flops 9221, 9121, 9122, 9222, 9223, 9123, 9124, 9224, 9225, 9125,9126, 9226, 9227, 9127, 9128, and 9228.

FIG. 9B is a schematic diagram of a test pattern generator for on-chiptest generation in accordance with some embodiments. The D flip-flop 901has an output 902, which is fed to the input of an inverter 903. Theoutput 904 of the inverter is fed back to the input of the D flip-flop901. The output 902 can be used as the scan input 9301 in FIG. 9A. Inother embodiments, other test pattern generators are used.

FIG. 9C is a schematic diagram of a test response comparison unit foron-chip test generation and comparison in accordance with someembodiments. The scan output 910 is fed through the counter 905 as aninput 906 to the comparator 907. The other input 909 of the comparator907 is calculated based on scan length and the generated pattern. Thevalues of input 906 and input 909 are compared in the comparator 907,and the output 908 indicates whether the 3DIC passes or fails the scanchain test.

The embodiments in FIG. 1 through 9C can be combined with each other,the inclusion of one embodiment does not exclude the other embodiments.Although the examples described above include two dies for simplicity ofillustration, the methods and structures described herein can be appliedto 3DICs including more than two dies (e.g., four, six, or eight dies).

FIG. 10 is a schematic diagram of a deterministic circular built-inself-test architecture in accordance to some embodiments. The embodimentin FIG. 10 is similar to the embodiment in FIG. 9A. The upper die 10100is stacked on the top of the lower die 10200. According to someembodiments, there are eight flip-flops(10121, 10122, 10123, 10124,10125, 10126, 10127 and 10128) implemented in the upper die 10100, andthere are eight flip-flops(10221, 10222, 10223, 10224, 10225, 10226,10227 and 10228) in the lower die 10200. The eight flip-flops in theupper die 10100 and the eight flip-flops in the lower die 10200 areinter-connected in a similar fashion to those flip-flops shown in FIG.9A. The test and clock control unit 10110 in the upper die 10100 isconnected to the eight flip-flops in the upper die in a similar fashionto that of FIG. 9A. The difference between FIG. 10 and FIG. 9A is in thelower die 10200. The output 10255 of the eighth flip-flop 10228 in thelower die 10200 is connected to an inverter 10230. The output signalfrom flip-flop 10228 is inverted by the inverter 10230 and is thentransmitted to two different places: first, the inverted signal 10251 istransmitted back to the input of the first flip-flop 10221 of the lowerdie 10200; second, the inverted signal 10251 is transmitted to theanalyzer unit 10213 in the lower die 10200.

The test and clock control unit 10110 of the upper die 10100 isconnected to the clock control unit 10211 in the lower die 10200. Thephase lock loop (PLL) unit 10212 controls the clock and control unit10211. The output of the clock and control unit 10211 is alsotransmitted to the analyzer unit 10213 in the lower die 10200. The clockand control unit 10211 transmits clock signal to each of the eightflip-flops in the lower die 10200. The clock and control unit 10211 alsotransmits set and rest signals to each of the eight flip-flops in thelower die 10200. The set and rest signals are implemented to initializethe flip-flops. The analyzer unit 10213 accepts signals from theflip-flop scan chain and the clock and control unit 10211 to performanalytical tasks to diagnose the types of the faults present in theflip-flop scan chain and to locate such faults therein. The scan path10900 includes a continuously connected set of latches andinterconnections between and within dies, for shifting data from thescan input to the scan output. According to some embodiments, the scanpath 10900 includes flip-flop 10221, interconnect 10301, flip-flop10121, connect 10151, flip-flop 10122, interconnect 10302, flip-flop10222, connect 10252, flip-flop 10223, interconnect 10303, flip-flop10123, connect 10152, flip-flop 10124, interconnect 10304, flip-flop10224, connect 10253, flip-flop 10225, interconnect 10305, flip-flop10125, connect 10153, flip-flop 10126, interconnect 10306, flip-flop10226, connect 10254, flip-flop 10227, interconnect 10307, flip-flop10127, connect 10154, flip-flop 10128, interconnect 10308, flip-flop10228, output 10255, inverter 10230 that inverts the output signal, andconnect 10251 that feed the inverted output to the input of the firstflip-flop 10221 for form a scan path. The details of the analyzing anddiagnosing steps will be discussed below.

FIG. 11 is a block diagram of a deterministic circular built-inself-test architecture in accordance with some embodiments. Thedeterministic circular built-in self-test architecture 11000 includes aplurality of interconnect segments, labeled as interconnect segment 1(11100), through interconnect segment X (11200). The deterministiccircular built-in self-test architecture 11000 also includes amultiplexer 11300, a first counter unit 11301 for counting the number ofhold violations, a second counter unit 11302 for counting the number ofsetup violations, a compare unit 11303 for comparing the output of thefirst counter unit 11301 and the output of the second counter unit11302. According to some embodiments, a hold violation happens when theflip-flop holds the old value and cannot change from 1 to 0, or from 0to 1 when it is supposed to change. According to some embodiments, asetup violation happens when the new data comes to a flip-flop earlierthan the new data is supposed to be there. The deterministic circularbuilt-in self-test architecture 11000 further includes a control logicunit 11304, a test access port (TAP) unit 11305, a phase lock loop (PLL)unit 11306, a clock controller 11307, and a single pulse unit 11308. TheTAP unit 11305 is connected to a JTAG bus. A JTAG bus is the StandardTest Access Port and Boundary Scan Architecture according to IEEEstandard 1149.1.

The first interconnect segment 11100 includes a first multiplexer 11101,a second multiplexer 11102, a plurality of flip-flops 11103, 11104,11105, 11106, 11107, 11108, 11109, 11110, and a diagnosis unit 11111.According to some embodiments, the first input 11101A of the firstmultiplexer 11101 is connected to the scan-in signal 11309, and thesecond input 11101B of the first multiplexer 11101 is connected to thesecond inputs of all subsequent interconnect segments, up to the secondinput 11201B of the first multiplexer 11201 of the Xth interconnectedsegment 11200. The output of the first multiplexer 11101 is connected tothe first input 11102A of the second multiplexer 11102, and the secondinput 11102B of the second multiplexer 11102 is connected to the QB (QBrepresents “Q bar”, the inversion of Q) output the last flip-flop11110QB. The output 11102C is connected to the D input 11103D of thefirst flip-flop 11103, and the Q output 11103Q is connected to the Dinput 11104D of the subsequent flip-flop 11104. The Q output of each ofthe flip-flops are connected to the D input of the subsequent flip-flopsin a similar way. The clock signal 11112 provide clock signal to each offlip-flops 11103, 11104, 11105, 11106, 11107, 11108, 11109 and 11110.The output 11110Q of the last flip-flop 11110 is transmitted as an inputto the multiplexer 11300. The output 11110Q of the last flip-flop 11110in the first interconnect segment 11100 is also connected to the firstinput of the first multiplexer in the second interconnect segment (notshown in the figure). The diagnosis unit 11111 further includes an ORgate 11111A as a setup detector, and a XOR gate 11111B as a holddetector. The detailed operations of OR gate 11111A as a setup detector,and a XOR gate 11111B as a hold detector is discussed in FIGS. 21 and 22.

All subsequent interconnect segments up to interconnect segment X 11200are configured similarly to the interconnect segment 1 11100. The secondinputs of the first multiplexers of the plurality of interconnectsegments from 1 to X are connected together. The Q outputs of the lastflip-flops in each of the plurality of flip-flops are transmitted to themultiplexer 11300 as inputs in a similar way to 11110Q. The output ofthe diagnosis units are also connected to the multiplexer 11300 in asimilar way to diagnosis unit 11111. The Q outputs of the lastflip-flops of each of the interconnect segment (except the lastinterconnect segment X) is connected to the first input of the firstmultiplexer in the subsequent interconnect segment.

The output 11300A is transmitted to both the first counter unit 11301and the second counter unit 11302 for counting hold setup faultrespectively. The output of the first counter unit 11301 and the secondcounter unit 11302 are transmitted to the compare unit 11303 forcomparison to determine pass or fail of the test, a detailed discussionregarding the test is presented in the description of FIG. 23 in thestep 2303. The output 11300B of the multiplexer 11300 is transmitted tothe control logic unit 11304 for further processing. The clock controlunit 11307 provides a first control signal 11307A to control the singlepulse unit 11308, a second control signal 11307B to provide clocksignals to all interconnect segments by connecting to the flip-flops’clock inputs in a similar way to clock signal 11112. The third controlsignal 11307C controls the first counter 11301 and the second counter11302.

The control logic unit 11304 provides a start and stop signal 11304A tocontrol the starting and stopping of the clock controller unit 11307.The control logic unit 11304 provides diagnosis signal 11304B connectingto the selector signals of the first multiplexers in each of theinterconnect segment for setup and hold diagnosis. The details of thesetup and hold diagnosis are discussed in the following figures. Thecontrol logic unit 11304 provides a set and rest signal 11304C to thesingle pulse unit 11308, the first counter unit 11301, the secondcounter unit 11302 and each of the flip-flops in each of theinterconnect segment. The control logic unit 11304 also provides aselector signal 11304D to control the selectors of the secondmultiplexers in each of the interconnect segments. In addition, thecontrol logic unit 11304 is also coupled to the first counter unit11301, the second counter unit 11302, and the TAP unit 11305, The PLLunit 11306 accepts an external slow clock to control the clockcontroller 11307.

FIG. 12 is a schematic diagram of a fault free circuit of fourflip-flops and its corresponding logic table in accordance with someembodiments. There are four flip-flops 1201, 1202, 1203 and 1204 in theinterconnect segment 1205 according to some embodiments. According tosome embodiments, the interconnect segment 1205 is the firstinterconnect segment in FIG. 11 . The first flip-flop 1201’s output1201Q(Q1) is connected to the D input 1202D of the second flip-flop1202, the output 1202Q(Q2) is connected to the D input 1203D of thethird flip-flop, the Q output 1203Q(Q3) is connected to the D input1204D of the fourth flip-flop, the Q output of the fourth flip-flop 1204is 1204Q(Q4). The QB output 1204QB of the fourth flip-flop 1204 isconnected to the D input of the first flip-flop 1201. QB means Q-bar, orthe inversion of Q. The Set signals “S” of all of the four flip-flopsare connected to Set signal 11304C of the control logic unit 11304illustrated in FIG. 11 . Similarly, the Reset signal “R” of all of thefour flip-flops are connected to the Reset signal 11304C of the controllogic unit 11034 illustrated in FIG. 11 . The clock of all of theflip-flops are controlled by the clock signal 11307B of the clockcontroller unit 11307 illustrated in FIG. 11 .

According to some embodiments, the circuit implemented by flip-flops1201 through 1204 is a fault-free circuit. According to someembodiments, table 120 is a table illustrating the Q output values ofthe flip-flops 1201 through 1204 at clock cycles 0, 1, 2, 3, 4, 5, 6, 7and 8. According to some embodiments, for a circuit with N flip-flops,it takes 2N clock cycles to go back to its initial state, and thiscircuit is a 2N-state finite state machine. In FIG. 12 , N = 4, thus 2N= 8. Accordingly, the circuit with 4 flip-flops is a finite statemachine with 8 states. In Table 120, for each clock cycle 0 through 8,there are 4 Q values, Q1, Q2, Q3 and Q4 corresponding to the Q outputsof the flip-flops. At clock cycle 0, all Q values are 0, at clock cycle8, the circuit goes back to the initial state with all Q values equal to0. At clock cycle 1, the value 1 is shifted out on Q1; at clock cycleQ2, value ones are shifted out on Q1 and A2; at clock cycle 3, valueones are shifted out on Q1, Q2, and Q3; at clock cycle 4, value ones areshifted out on all Q’s from Q1 to Q4. At clock cycle 4, four value onesare shifted to the fault free circuit 1205. Because there is no fault inthe circuit 1205, it takes another 4 cycles for the circuit to returnback to its initial state with all Q values equal to 0. The outputsequence on Q4 during the 0 through 8 clock cycles are: 0, 0, 0, 0, 1,1, 1, 1, 0, as illustrated in the last column in the Table 120 markedQ4. The number of zeroes and ones play a key role in the determinationof the fault states of the flip-flops in the interconnect segment 1205.According to some embodiments, for a fault-free circuit with Nflip-flops of 2N cycles, there are N ones and N zeroes in the Q outputof the last flip-flop. In the fault-free circuit example illustrated inFIG. 12 , the 8 cycles in the Q4 data has 4 zeroes and 4 ones.

FIG. 13 is a schematic diagram of a circuit with a stuck-at-1 fault at afirst location of four flip-flops and its corresponding logic table inaccordance with some embodiments. FIG. 13 illustrates a similarconfiguration to FIG. 12 , with the interconnect 1305 including fourflip-flops 1301, 1302, 1303 and 1304. FIG. 13 is different from FIG. 12in that there is a stuck-at-1 (SA1) fault at the first flip-flop 1301,as illustrated as SA1 in FIG. 13 . The SA1 fault could be at D1, betweenD1 and Q1 or at Q1. The “Reset” signal resets the output of theflip-flops to 1 at appropriate clock cycles.

Similarly, the Table 130 illustrates the Q output states of theflip-flops 1301 through 1304 from clock cycles 0 through 8. When thecircuit is not fault-free, as illustrated in FIG. 12 , the circuit is nolonger a finite state machine and the circuit does not go back to itsinitial state after 2N cycles. The number of ones and number of zeroesare no longer equal in the Q4 output from clock cycles 1 through 8.According to some embodiments, for 2N cycles, there are N-1 zeros andN+1 ones on the Q4 output. As illustrated in the Table 130, becausethere is an SA1 fault at flip-flop 1301, the Q output value Q1 is“stuck-at” 1, which propagates to the next flip-flop at the next clockcycle. For the rest of the 8 clock cycles, the Q1 value remains at 1.Once Q2 reaches 1, the 1 also propagates to the next flip-flop afteranother clock cycle. Eventually the value 1 reaches Q4 and because Q1 is“stuck at” 1, it keeps Q2, Q3 and Q4 all at the value 1 after 4 clockcycles. After 8 clock cycles, the number of ones is 4+1=5, and thenumber of zero’s is 4-1=3.

FIG. 14 is a schematic diagram of a circuit with a stuck-at-1 fault at asecond location of four flip-flops and its corresponding logic table inaccordance with some embodiments. FIG. 14 illustrates another similarconfiguration 1405 with four flip-flops 1401, 1402, 1403 and 1404, andthe difference between FIG. 14 and FIG. 13 is that there is a Stuck-At-1fault at a second location in FIG. 14 .

The difference between the Tables 140 and 130 is that instead of Q1being stuck at 1 for all 8 clock cycles, as in the Table 130, in Table140, Q2 is stuck at 1 for all 8 clock cycles. According to someembodiments, there are N-2 zeroes and N+2 ones in the Q4 output after 2Nclock cycles. Similar to FIG. 13 , the configuration in FIG. 14 is not a2N finite state machine either. According to some embodiments, when N =4, there are two (4-2=2) zero’s and six (4+2=6) ones in the Q4 output.

FIG. 15 is a schematic diagram of a circuit with a stuck-at-1 fault at athird location of four flip-flops and its corresponding logic table inaccordance with some embodiments. Another stuck-at-1 fault at a thirdlocation is illustrated in FIG. 15 in a similar configuration ofinterconnect segment 1505 that includes four flip-flops 1501, 1502, 1503and 1504. The difference between the Table 150 and the Table 130 is thatQ3 values are stuck at 1 for all eight clock cycles. According to someembodiments, there are N-3 zero’s and N+3 ones in the Q4 output data for2N clock cycles. The interconnect segment configuration 1505 is not afinite state machine and the circuit does not go back to its initialstate. When N is equal to 4 as illustrated in FIG. 15 , there are one(4-3=1) zero and seven (4+3=7) ones for Q4 in the Table 150.

FIG. 16 is a schematic diagram of a circuit with a stuck-at-1 fault at afourth location of four flip-flops and its corresponding logic table inaccordance with some embodiments. Another stuck-at-1 fault isillustrated at a fourth location illustrated in FIG. 16 in a similarconfiguration of interconnect segment 1605 that includes four flip-flops1601, 1602, 1603 and 1604. The difference between the Table 160 and theTable 130 is that Q4 values are stuck at 1 for all eight clock cycles.According to some embodiments, there are N-4 zeroes and N+4 ones in theQ4 output data for 2N clock cycles. The interconnect segmentconfiguration 1605 is not a finite state machine and the circuit doesnot go back to its initial state. When N is equal to 4 as illustrated inFIG. 16 , there are zero (4-4=0) zero and eight (4+4=8) ones for Q4 inthe Table 160.

In summary, for a fault-free flip-flop chain of length N, there areequal numbers of zeroes and ones after 2N clock cycles. When theflip-flop chain is initialized to all zeroes (which is called “reset”),after 2N cycles, if the number of ones is larger than the number ofzeroes on the output of the last flip-flop, a conclusion can be drawnthat there is a stuck-at-1 fault in the flip-flop chain path. Thelocation of the stuck-at-1 fault can be further identified by the numberof ones observed at the last flip-flop (QN, the Q output of the Nthflip-flop). If the number of ones is 2N, then the stuck-at-1 fault is atthe input of the last (or N-th) flip-flop in the flip-flop chain; if thenumber of ones is 2N-1, then the stuck-at-1 fault is at the input of the(N-1)-th flip-flop; if the number of ones is 2N-2, then the stuck-at-1fault is at the input of the (N-2)-th flip-flop; if the number of onesis N+1, then there is either a stuck-at-1 fault, or a setup violation atthe first flip-flop of the flip-flop scan chain.

If the number of ones is smaller than the number of zeroes, then thereis a setup/hold violation in the flip-flop chain. A hold violationhappens when the flip-flop holds the old value and cannot change from 1to 0, or from 0 to 1 when it is supposed to change. A setup violationhappens when the new data comes to a flip-flop earlier than the new datais supposed to be there.

When the number of zero’s is equal to 2N, then there is a stuck-at-0fault in the flip-flop scan chain. The location of the stuck-at-0 faultcan be located by initializing the flip-flop scan chain to ones.

FIG. 17 is a schematic diagram of a circuit with a stuck-at-0 fault at afirst location of four flip-flops and its corresponding logic table inaccordance with some embodiments. Similar to FIG. 13 discussed above,the interconnect segment 1705 includes four flip-flops 1701, 702, 1703and 1704. The first difference is that a “Set” signal sets the output ofthe flip-flops to 0 at appropriate clock cycles. the second differenceis that, instead of a stuck-at-1 fault, a stuck-at-0 fault is located atthe first flip-flop 1701. The Table 170 is similarly structured as theTable 130. At clock cycle 0, all flip-flops are initialized to 1, thenat clock cycle 1, 0 is “Set” to the first flip-flop 1701, at eachsubsequent clock cycle, 0 is “set” to an additional subsequent flip-flopin the chain. It is clear by comparing the Tables 130 and 170, that theTable 170 is a reverse of the Table 130 because when all ones are placedby zeroes, and zeroes by ones, in Table 170, it becomes identical toTable 130, and vice versa. According to some embodiments, when thestuck-at-0 fault is located between the first flip-flop 1701 and thesecond flip-flop 1702, a corresponding table can be derived by reversingthe Table 140. Following the same logic, when the stuck-at-0 fault islocated between the second flip-flop 1702 and the third flip-flop 1703,a corresponding table can be derived by reversing the Table 150; whenthe stuck-at-0 fault is located between the third flip-flop 1703 and thefourth flip-flop 1704, a corresponding table can be derived by reversingthe Table 160.

Similar to the method for determining the existence and location of thestuck-at-1 fault discussed above, a method for determining the existenceand location of the stuck-at-0 fault is discussed below.

The first step is the determination of the existence of the stuck-at-0fault. When the number of ones is smaller than the number of zeroes,then there is a stuck-at-0 fault in the flip-flop scan chain path. Thenthe location of the stuck-at-0 fault can be further determined by thenumber of zero’s observed at the last flip-flop. Similar to the settingdiscussed above, assuming there are N flip-flops in the scan chain, ifthe number of zeroes is 2N, then the stuck-at-0 fault is located at theinput of the last flip-flop (or the N-th flip-flop); if the number ofzeroes is 2N-l , then the stuck-at-0 fault is located at the input ofthe (N-1)-th flip-flop in the scan chain; if the number of zeroes is2N-2, then the stuck-at-0 fault is located at the input of the (N-2)-thflip-flop in the scan chain; if the number of zeroes is N+1, then thestuck-at-0 fault is located at the input of the first flip-flop in thescan chain.

According to some embodiments, if the number of ones is larger than thenumber of zeroes, then there is a stuck-at-1 fault and its location canbe determined by initializing the scan chain to all zeroes and thenimplementing the method discussed following FIG. 16 .

FIG. 18 is a logic table of a circuit with 7 flip-flops under holdfaults in accordance with some embodiments. A hold violation, or a holdfault, happens when a certain flip-flop cannot hold data for a longenough period of time (e.g., because of a delayed clock signal).Effectively, a single flip-flop hold violation is equivalent to a scanchain of one bit shorter as illustrated in FIG. 21 below. In order todetect a hold violation, the entire flip-flop scan chain of length N isinitialized to all zeroes and then the test run for 2 N cycles. If thenumber of ones is smaller than the number of zeroes observed on the lastflip-flop, then there is a hold fault (or a setup fault as illustratedin FIG. 19 ) in the flip-flop scan chain. In the example illustrated inTable 180, the flip-flop scan chain has 7 flip-flops (N = 7). After 14(2 N) clock cycles, six ones and 8 zeroes are observed on the last (7th)flip-flop. Because the number (6) of ones is smaller than the number (8)of zeroes, a possible hold fault is detected in the flip-flop chain.

FIG. 19 is a logic table of a circuit with 7 flip-flops under setupfaults in accordance with some embodiments. A setup violation, or asetup fault, happens when the data in the flip-flop arrives earlier thanit is supposed to. Effectively, a single flip-flop setup violation isequivalent to a scan chain of one bit longer as illustrated in FIG. 22below. Using a similar method to that discussed above for FIG. 18 , theentire flip-flop scan chain is initialized to zeroes, after 2 N clockcycles, if the number of ones is smaller than the number of zeroes, thenthere is either a setup fault or a hold fault in the scan chain. In theexample illustrated in Table 190, the flip-flop scan chain has 7flip-flops (N = 7). After 14 (2 N) clock cycles, six ones and 8 zeroesare observed on the last (7th) flip-flop. Because the number (6) of onesis smaller than the number (8) of zeroes, a possible setup fault isdetected in the flip-flop chain. According to some embodiments, themethods illustrated in FIG. 18 and FIG. 19 produce the same results forboth hold and setup faults, so additional steps are implemented todifferentiate setup fault and hold fault after the number of ones isdetermined to be smaller than the number of zeroes after 2 N clockcycles on the last flip-flop.

According to some embodiments, a ring counter is a type of countercomposed of a type of circular shift register. The output of the lastshift register is fed to the input of the first register. A Johnsoncounter is a ring counter with an inversion. The interconnect segmentsillustrated in FIGS. 12-17 are all Johnson counters because the QB(Q-bar, the inversion of the Q output) is fed to the input of the firstflip-flop.

According to some embodiments, the Johnson counter is implemented todiagnose setup and hold faults. According to some embodiments, built-inself-test (BIST) based solutions are implemented to meet scan out timingand high speed scan shift clock specifications.

FIG. 20 is a schematic diagram of a fault-free on-chip scan-chain with 7flip-flops and its corresponding logic waveforms in accordance with someembodiments. According to some embodiments, seven flip-flops 2001through 2007 are implemented in the flip-flop scan chain, and eachflip-flop has a D input (e.g., 2001D), a Q output (e.g., 2001Q), a clock(e.g., 2001CLK), and a reset (e.g., 2001CLR). In the case of the lastflip-flop, there is an additional QB (Q-bar, the inversion of Q) signalfor implementation of Johnson Counter. A signal pulse generator unit2010 generates clock signals for all flip-flops in the flip-flop scanchain, a line 200 connects the single pulse generator unit 2010 with thefirst flip-flop 2001, and connects each flip-flop with its successor(except the last one). Signal 2021 is the clock signal and signal 2022is the corresponding shift chain. Signal 2023 is the initial pulsesignal generated by the single pulse generator unit 2010. Signals 2024,2025, 2026, 2027, 2028, 2029 and 2030 are the corresponding pulsesignals shifted along the flip-flop scan chain path. FIG. 20 is anillustration of a fault-free flip-flop scan chain in which there is nofault and there is one and only one flip-flop holding a value of one inany clock cycle.

FIG. 21 is a schematic diagram of an on-chip scan-chain having a holdviolation with 7 flip-flops and its corresponding logic waveforms inaccordance with some embodiments. According to some embodiments, FIG. 21illustrates a similar configuration to that shown in FIG. 20 , exceptthat there is a hold fault at the third flip-flop in FIG. 21 . Asdiscussed above, a scan chain with a hold fault is equivalent to a scanchain of one bit shorter. Similar to the description of FIG. 20 , signal2121 is the clock cycle signal and the signal 2122 is the shift signal.The signals 2123 through 2130 are the signals observed on the flip-flops2101 through 2107. The signal 2131 is a logic XOR of signals 2123through 2130. Between the signal 2126 and the signal 2127, there is anoverlap. Accordingly, the XOR signal 2131 produces a pulse at thecorresponding location and the shift counter is frozen on this signal.As a result, the value of the shift counter identifies the location ofthe flip-flop (i.e., the third flip-flop) with the hold fault. Accordingto some embodiments, long flip-flop scan chains can be divided intoshorter chains with one flip-flop overlap to reduce XOR tree timingimpact.

FIG. 22 is a schematic diagram of an on-chip scan-chain having a setupviolation with 7 flip-flops and its corresponding logic waveforms inaccordance with some embodiments. According to some embodiments, FIG. 22illustrates a similar configuration as FIG. 20 except that there is asetup fault at the fourth flip-flop. As discussed above, a scan chainwith a setup fault is equivalent to a scan chain of one bit longer.Similar to the discussion in FIG. 20 , signal 2221 is the clock cyclesignal and the signal 2222 is the shift signal. The signals 2223 through2230 are the signals observed on the flip-flops 2201 through 2207. Thesignal 2231 is a logic OR of signals 2223 through 2230. Between thesignal 2226 and the signal 2227, the OR signal 2231 produces a pulse atthe corresponding location and the shift counter is frozen on thissignal. As a result, the value of the shift counter identifies thelocation of the flip-flop (i.e., the third flip-flop) with the setupfault. According to some embodiments, similar to the discussion in FIG.21 , long flip-flop scan chains can be divided into shorter chains withone flip-flop overlap to reduce OR tree timing impact.

FIG. 23 is a flowchart illustrating the method for deterministiccircular built-in self-test in accordance with some embodiments.According to some embodiments, the flow-chart in FIG. 23 summarizes thediscussion of the method above. According to some embodiments, themethod for deterministic circular built-in self-test is implemented onthe circuit structure illustrated in FIG. 11 .

According to some embodiments, at the step 2301, the deterministiccircular built-in self-test circuit 11100 in FIG. 11 is switched topass/fail mode by the control logic unit 11034. At step 2302, thecontrol logic unit 11304 selects the interconnect segment under testthrough the controlling of multiplexers 11102B through 11202B. Once aninterconnect segment is selected, for example the interconnect segment11100, at step 2303, the deterministic circular self-test is run byinitializing all flip-flops in the scan chain to zeroes. Then ones areshifted in consecutively for 2 N clock cycles, where N is the number offlip-flops in the scan chain of the interconnect segment. At step 2304,a comparison is conducted between the number of ones and number ofzeroes observed on the last flip-flop to determine whether the testresult is a pass or fail. At the step 2305, if the number of ones andzeroes are equal, then no fault is detected and the selectedinterconnected segment is a fault free circuit. If the numbers of onesand zeroes are not equal, at the step 2306, the circuit 11100 isswitched to diagnosis mode and a determination of stuck-at-1 fault orstuck-at-0 fault is conducted. At step 2307, if the number of ones islarger than the number of zeroes, then there is a stuck-at-1 fault inthe path of the selected interconnect segment. At step 2308, thelocation of the stuck-at-1 fault is determined. At step 2309, if thenumber of zeroes is equal to 2N, then there is a stuck-at-0 fault in thescan chain of the selected interconnected segment. At step 2310, thelocation of the stuck-at-0 fault is determined. At step 2309, if thenumber of ones is smaller than the number of zeroes, then there is asetup or hold fault. Then at step 2311, the method determines whetherthere is a setup fault or a hold fault in the scan chain. At step 2311,the scan chain is initialized to ones, and zeroes are shifted inconsecutively for 2N clock cycles, where N is the number of flip-flopsin the scan chain of the interconnect segment. A comparison is conductedbetween the number of ones and number of zeroes observed on the lastflip-flop. The diagnosis unit 11111 is activated to determine whetherthere is a setup fault or a hold fault according to the methods shown inFIG. 21 and FIG. 22 . At step 2312, by using the OR gate 11211A, thenon-zero output signal on the OR gate 11211A produces the location of asetup fault; at step 2313, by using the XOR gate 11211B, the non-zerooutput signal on the XOR gate 11211B produces the location of a holdfault. According to some embodiments, the above steps are repeated foreach of the interconnect segments in the circuit 11100 in FIG. 11 todetermine the types of faults in each of the interconnect segment andthe location of each fault.

Various embodiments using the concepts provided herein can use clocksynchronization with a single clock speed to ensure shift testingwithout requiring complex synchronization of two clocks or at-speedtransition generation. This method allows use of a single pass flow forboth DC and AC testing. The method can provide testing of actualfunctional inter-die connections (i.e., connections that are used duringoperations other than scan chain testing) as part of the scan chainshift test. Embodiments of this disclosure are suitable for designs withlarge or small numbers of interconnects. Although examples are describedabove using 3DICs with hybrid bonding, the architecture and methodsdescribed herein can be applied to any 3DIC and to any 2.5D IC (with aninterposer).

In some embodiments, a device comprises: a first die having disposedthereon a first plurality of latches wherein ones of the first pluralityof latches are operatively connected to an adjacent one of the firstplurality of latches; and a second die having disposed thereon a secondplurality of latches wherein ones of the second plurality of latches areoperatively connected to an adjacent one of the second plurality oflatches. Each latch of the first plurality of latches on said first diecorresponds to a latch in the second plurality of latches on said seconddie. Each set of corresponding latches are operatively connected. A scanpath comprises a closed loop comprising each of said first and secondplurality of latches. One of the second plurality of latches isoperatively connected to another one of the second plurality of latchesvia an inverter.

In some embodiments, a device comprises a first die and a second diewith interconnections between the first die and the second die. Each ofthe first and second dies comprises: a plurality of latches, including arespective latch corresponding to each one of the interconnections; anda plurality of multiplexers. Each multiplexer is connected to arespective one of the plurality of latches and a respective functionalpath. Respective ones of the plurality of multiplexers in the first dieare connected to a subset of latches within the plurality of latches inone of the first die and the second die. The subset of latches arenon-adjacent from each other among the plurality of latches. A scan pathcomprises a closed loop comprising each of the plurality of latches inthe first and second dies.

In some embodiments, a device comprises a first die and a second die. Atleast one of the first die and second die includes level shifters andinterconnections between the first die and the second die. Each of thefirst and second dies comprises: a plurality of latches, including arespective latch corresponding to each one of the interconnections, anda plurality of multiplexers. Each multiplexer is connected to arespective one of the plurality of latches and a respective functionalpath and is arranged for receiving and selecting one of a scan testpattern or a signal from the functional path for outputting during ascan chain test of the first die and second die. The plurality oflatches in the first die includes a first latch without a connection toa multiplexer. A scan path comprises a closed loop comprising each ofthe plurality of latches in the first and second dies.

The foregoing .outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a first die having disposedthereon a first plurality of latches; and a second die having disposedthereon a second plurality of latches, wherein: each latch of the firstplurality of latches on said first die operatively couple to arespective latch in the second plurality of latches on said second die,a scan path comprises a closed loop comprising a first latch in thefirst plurality of latches in the first die, a second latch in thesecond plurality of latches in the second die, a third latch in thesecond plurality of latches in the second die, and a fourth latch in thefirst plurality of latches in the first die, the first latch and thefourth latch are adjacent to each other in the first die, and the secondlatch and the third latch are adjacent to each other in the second die.2. The device of claim 1, wherein the second die further comprises aclock and control unit.
 3. The device of claim 1, wherein the second diefurther comprises a phase lock loop unit.
 4. The device of claim 1,wherein the second die further comprises an analyzer unit.
 5. The deviceof claim 1, wherein the first plurality of latches and the secondplurality of latches comprise D flip-flops.
 6. The device of claim 1,further comprising a plurality of level shifters for changing anamplitude of signals transmitted between the first die and the seconddie.
 7. The device of claim 1, wherein the first die has a first clockand the second die has a second clock, and the first clock and secondclock are synchronized with each other.
 8. The device of claim 1,wherein the first plurality of latches in the first die and the secondplurality of latches in the second die are not of the same type.
 9. Thedevice of claim 1, wherein the first plurality of latches includes asubset of latches, each latch in the subset transmitting a signal fromthe first die to a corresponding latch in the second die.
 10. The deviceof claim 1, wherein: the first plurality of latches includes a firstnumber of latches; the second plurality of latches includes a secondnumber of latches; and the first and second numbers are different fromeach other.
 11. A device, comprising: a first die; and a second die,wherein each of the first and second dies comprises: a plurality oflatches; and a plurality of multiplexers, each multiplexer connected toa respective one of the plurality of latches, wherein respective ones ofthe plurality of multiplexers in the first die are connected to a subsetof latches within the plurality of latches in one of the first die andthe second die, wherein a scan path comprises a closed loop comprising afirst latch in the first die, a second latch in the second die, a thirdlatch in the second die, and a fourth latch in the first die, whereinthe first latch and the fourth latch are adjacent to each other in thefirst die, wherein the second latch and the third latch are adjacent toeach other in the second die.
 12. The device of claim 11, wherein theplurality of latches in the first die and the second die include Dflip-flops.
 13. The device of claim 11, wherein respective ones of theplurality of multiplexers are connected to alternating ones of theplurality of latches in the first die.
 14. The device of claim 11,wherein a respective one of the plurality of multiplexers receives oneinput from a corresponding one of the plurality of latches in the firstdie, receives another input from a functional path in the first die, andtransmits an output to a corresponding one of the plurality of latchesin the second die.
 15. The device of claim 11, wherein one of theplurality of latches in the first die is connected to output a signal toone of the plurality of multiplexers in the second die and receives aninput signal from an adjacent latch in the plurality of latches withinthe first die, wherein the adjacent latch does not output a signal toany of the plurality of multiplexers in the second die.
 16. The deviceof claim 11, wherein the plurality of latches includes a subset of theplurality of latches, each latch in the subset transmitting a signalfrom one of the first and second dies to a corresponding latch in theother of the first and second dies, and each latch in the subset isconnected to a first input of a corresponding one of the plurality ofmultiplexers.
 17. A device, comprising: a first die; and a second die,at least one of the first die and second die including interconnectionsbetween the first die and the second die, wherein each of the first andsecond dies comprises a plurality of latches, including a respectivelatch corresponding to each one of the interconnections, a scan pathcomprises a closed loop comprising at least two latches in the pluralityof latches in the first die and at least two latches in the plurality oflatches in the second die, the at least two latches in the plurality oflatches in the first die are adjacent to each other, and the at leasttwo latches in the plurality of latches in the second die are adjacentto each other.
 18. The device of claim 17, wherein the plurality oflatches are connected in a chain having a first scan chain output, andan output of at least one latch other than a last one of the pluralityof latches is transmitted to a second scan chain output.
 19. The deviceof claim 17, wherein each of the first and second dies furthercomprises: a plurality of multiplexers, each multiplexer connected to arespective one of the plurality of latches, wherein respective ones ofthe plurality of multiplexers in the first die are connected to a subsetof latches within the plurality of latches in one of the first die andthe second die.
 20. The device of claim 19, wherein two or more of theplurality of multiplexers have taps for outputting signals from thedevice.